1. Field of the Invention
The present invention is generally related to a system for controlling air flow into an internal combustion engine and, more particularly, to a system which monitors air flow into an engine and modifies a throttle position to optimize the scavenging air flow according to a preselected schedule based on the load on the engine and engine speed.
2. Description of the Prior Art
Many different types of fuel delivery systems are known to those skilled in the art. In addition, many types of control systems are known which vary either the fuel or the air supplied to an internal combustion engine to affect its operation.
U.S. Pat. No. 4,969,435, which issue Morikawa et al on Nov. 13, 1990, describes an idle speed control system for a two cycle engine. The engine has a scavenged pump provided in an intake passage and a fuel/air injection provided for injecting fuel directly in a cylinder of the engine together with air. A control unit has a calculator for calculating quantities of fuel and air injected from the fuel/air injector and for producing a fuel injection pulse width signal and an air injection pulse width signal based on the calculated quantities. Engine speed at idling state is compared with a desired idle speed and an error signal is produced. At least one of the pulse width signals is corrected with a correction value for controlling the injection quantity so as to cause the idle speed to converge to the desired idle speed.
U.S. Pat. No. 4,995,354, which issued to Morikawa on Feb. 26, 1991, discloses a two cycle engine which has a fuel inject, scavenge port and an exhaust port which is provided with a scavenge pump for supplying scavenging air into a cylinder. An exhaust rotary valve is connected to the exhaust port to open and close the port. Similarly, a scavenge rotary valve is connected to the scavenge port to open and close the port. Engine operating condition including engine speed and degree of depressing the accelerator pedal, representing the engine load, is inputted to a control unit, which variably controls the timings of opening and closing the exhaust and scavenge rotary valves in accordance with the engine operating condition.
U.S. Pat. No. 5,848,582, which issued to Ehlers et al on Dec. 15, 1998, discloses an internal combustion engine with barometric pressure related start of air compensation for a fuel injector. The control system for a fuel injector system for an internal combustion engine is provided with a method by which the magnitude of the start of air point for the injector system is modified according to the barometric pressure measured in a region surrounding the engine. This offset, or modification, of the start of air point adjusts the timing of the fuel injector system to suit different altitudes at which the engine may be operating.
U.S. Pat. No. 5,540,205, which issued to Davis et al on Jul. 30, 1996, describes an air fuel ratio control system. The method of controlling the mass of air delivered to an internal combustion engine per cylinder, per cycle, by utilizing a unique control algorithm is described.
U.S. Pat. No. 5,609,021, which issued to Ma on Mar. 11, 1997, describes the operation of an internal combustion engine. A method is described for operating an internal combustion engine burning a fuel containing carbon and hydrogen to provide a flame in the exhaust system to heat a catalytic converter or burn off the soot in a particulate filter trap. The method involves reducing the intake throttle opening during deceleration mode below the throttle opening for the steady speed idle position to create a proportion of combustible gases in the exhaust gas stream. By ensuring at the same time the presence in the exhaust gas stream of additional air, an ignitable mixture is produced which is ignited to burn as a flame in an afterburner chamber of the exhaust system. By selecting deceleration periods to enrich the mixture excessively in this manner, adverse effects on drivability are unnoticed.
U.S. Pat. No. 4,173,203, which issued to Nakaijima et al on Nov. 6, 1979, discloses an engine system. The engine system comprises an internal combustion engine, an air admission system to admit scavenging air, under pressure, into an engine cylinder through an additional intake valve and an EGR system. The air admission system includes an air pump and an EGR (exhaust gas recirculation) conduit of the EGR system having an inlet end connected to the engine exhaust conduit and an outlet end connected to the air admissions system upstream of the air pump to effect admission of recirculated exhaust gas through the additional intake valve together with scavenging air. With this EGR system and the replacement of residual gas with scavenging air, the rate of exhaust gas in the engine cylinder upon ignition is kept substantially constant over varying partial loads.
U.S. Pat. No. 4,192,262, which issued to Onoda et al on Mar. 11, 1980, describes a control system for varying the amount of scavenging air to be admitted to internal combustion engines. The control system is adapted for an internal combustion engine in which a jet of air is injected into each combustion chamber via a second intake valve during each exhaust cycle and the subsequent intake cycle. The system comprises a source of compressed air having a pressure to be varied in accordance with the engine speed, an injection passageway leading from the source toward each second intake valve and a flow controller operated in accordance with changes in intake manifold vacuum. The flow controller includes a scheduled flow area therethrough to increase, under conditions in which the engine speed is constant, the amount of air passing through the injection passageway in accordance with increasing engine load in such a way so as to increase the ratio of air flow through the injection passageway to the intake airflow to the engine under light engine load in order to cope with increasing residual gas fraction within each combustion chamber when the engine idles or operates under deceleration of the vehicle.
U.S. Pat. No. 4,185,599, which issued to Onoda et al on Jan. 29, 1980, describes a control system for varying the amount of scavenging air to be admitted to internal combustion engines. The control system is adapted for an internal combustion engine in which a jet of air is injected into a combustion chamber via a second intake valve during a period overlapping an exhaust cycle and the subsequent intake cycle for expelling residual gas within the combustion chamber in order to reduce residual gas fraction of charge for the subsequent combustion within the combustion chamber. The system comprises a source of compressed air having a constant pressure, an injection passageway leading from the source toward the second intake valve, a flow control valve fluidly disposed in the injection passageway, and means whereby the flow control valve will vary effective flow area of the injection passageway in response to a signal indicative of the flow rate of fluid passing through the engine induction passageway.
U.S. Pat. No. 5,832,895, which issued to Takahashi et al on Nov. 10, 1998, describes a control system for an internal combustion engine. The control system is for an internal combustion engine having an air intake amount regulating device and a fuel supply device. The control system comprises a device for detecting an engine operating condition of the engine, and a control unit. The control unit is configured to perform the steps of calculating a base fuel supply of fuel to be supplied to a combustion chamber of the engine in accordance with the engine operating, calculating a lean limit air-fuel ratio in accordance with the engine operating condition, stable combustion in the combustion being impossible at the air-fuel ratio leaner than the lean limit air-fuel ratio, calculating a target intake air amount of intake air to be supplied to the combustion chamber, required for meeting the basic fuel supply amount and the lean limit air-fuel ratio, controlling the intake air amount regulating device so as to regulate an intake air amount of the intake air to the target intake air amount and controlling the fuel supply device so as to regulate a fuel supply amount of the fuel to realize the lean limit air-fuel ratio, within a first engine operating condition (such as an idle condition) which is within a predetermined low range in engine speed and in engine load, and controlling the intake air amount regulating device so as to increase the intake air amount to fall within a high range between the maximum level and a level lower a predetermined amount than the maximum level and controlling fuel supply device so as to supply the fuel such that the air-fuel ratio falls within a predetermined range, within a second engine operating condition which is higher in at least one of engine speed and engine load than the first engine operating condition.
U.S. Pat. No. 5,054,444, which issued to Morikawa on Oct. 8, 1991, describes a fuel injection control system for a two cycle engine. The two cycle engine has a fuel injector provided for injecting fuel directly into a cylinder of the engine. An amount of air actually induced into the cylinder is calculated based on the amount of escape air and the amount of intake air detected by an air-flow meter. The quantity of fuel injected by the fuel injector is calculated based on the engine speed and the amount of air induced in the cylinder. The timing of the fuel injection is advanced as engine load increases and the duration of fuel injection increases as the engine load and engine speed increase.
U.S. Pat. No. 4,668,199, which issued Freund et al on May 26, 1987, discloses an idle exhaust relief system for outboard motors. The invention is an exhaust system for an outboard motor which includes a main exhaust passageway extending through a partially water filled chamber in the drive shaft housing. An inlet idle relief passage connects the top of the chamber with the main exhaust passageway and an outlet passage connects the top of the chamber with the atmosphere. The system thus defines an effective exhaust silencer for the idle exhaust.
U.S. Pat. No. 5,595,515, which issued to Hasegawa et al on Jan. 21, 1997, describes an outboard motor exhaust system which includes a simplified above-the-water exhaust gas discharge which is formed by an inverted U-shaped tube that is detachably connected into the outer casing of the driveshaft housing so that the outer casing need not be form with special passages for providing for exhaust gas flow.
U.S. Pat. No. 4,289,094, which issued to Tanahashi on Sep. 15, 1981, discloses a two cycle gasoline engine. The engine has a first scavenging port which is supplied with fuel-air mixture through a mixture passage, and a second scavenging port which is supplied with air, wherein supply of fuel-air mixture through the mixture passage is substantially throttled while supply of air through the second scavenging port is interrupted, so as to perform stratified scavenging, when the engine is operating at low load, while in medium to high load operation the throttling of the mixture passage is released while air is injected through said second scavenging port, so as to generate swirling of mixture charged in the cylinder chamber.
U.S. Pat. No. 5,259,344, which issued to Huang et al on Nov. 9, 1993, discloses an intermittent fuel-injection method and device for a two stroke engine. The method for a two stroke engine, which is done by means of an injection nozzle mounted under a cylinder head or on cylinder wall so as to have fuel directly injected into a cylinder to mix the air inside the cylinder into a homogeneous mixture includes a controller for use in controlling the fuel injection timing and quantity. The controller determines the injection timing and quantity in accordance with the engine intake airflow quantity and engine rpm. Under idle running conditions or low load running conditions, an intermittent fuel injection control method is used so as to enable an engine to perform one, two, three, four or five scavenging and exhaust cycles after one fuel injection cycle in order to obtain a steady and high combustion efficiency.
The above described patents are hereby explicitly incorporated by reference in this description of the present invention.
Those skilled in the art of internal combustion engines are familiar with many different techniques to regulate the air intake into the engine as a function of the fuel which is introduced into the combustion chambers of the engine. Some internal combustion engines incorporate fuel injection which can be a direct fuel injection (DFI) system that injects a mixture of fuel and air directly into the combustion chamber. In addition, those skilled in the art are familiar with many types of scavenging systems used in two cycle engines for the purpose of removing the exhaust products from the combustion chambers following the ignition of the fuel and air mixture within the combustion chamber. Some scavenging systems use auxiliary pumps to provide additional scavenging air into the combustion chambers.
In an engine that provides a stratified charge within a combustion chamber, the magnitude of pollutants within the exhaust stream from a combustion chamber does not vary directly with the magnitude of scavenging air at all rates of airflow provided to the combustion chamber following ignition. Instead, there exists an optimum rate of air flow of scavenging air which results in a minimum amount of unburned hydrocarbons in the exhaust steam. For a specific airflow, a minimum level of exhaust pollutants can be achieved, with greater amounts of exhaust pollutants at both lesser and greater magnitudes of airflow. This optimum air flow magnitude varies as a function of load on the engine and engine speed.
In internal combustion engines used for marine propulsion systems, an additional variable, which is dependant on the magnitude of air intake, must be considered. Many types of marine propulsion systems direct the exhaust products through the hub of a propeller to be exhausted beneath the water level of the body of water in which the marine vessel is operated. Generally, these marine systems also provide an idle relief port, or alternate exhaust port, in addition to the exhaust path through the propeller hub. When the marine propulsion system is operated in reverse gear, exhaust products emanating from the propeller hub are drawn back into the region of the rotating propeller blades. This extreme aeration of the propeller blade region seriously affects the efficiency of the marine propulsion system when operated in reverse gear and deleteriously affects the efficiency of the system.
The amount of exhaust products emanating through the propeller hub is directly affected by the amount of air introduced into the combustion chamber of the engine. Very high rates of intake air flowing into the combustion chamber will result in an exhaust stream of increased pressure and flow rate. This increased pressure and flow will cause a higher percentage of the exhaust stream to flow through the propeller hub below the surface of the water. Lower pressures and flow rates of the exhaust stream will result in a higher percentage of exhaust passing through the idle exhaust relief ports above water and away from the propeller blades and, as a result, the extreme aeration of the propeller blades during reverse operation of the marine propulsion system will be significantly less.
In view of the above, it can be seen that the amount of intake air provided to the cylinders of the internal combustion engine can affect the operation of the marine propulsion system in at least two ways. First, the amount of unburned hydrocarbons in the exhaust stream can be adversely affected if the scavenging air flow is either too low or too high. Secondly, the efficiency of the marine propulsion engine, when operated in reverse gear, can be adversely affected if the air intake flow rate is too high. It would therefore be significantly advantageous, particularly in internal combustion engines used for marine propulsion systems, if the air flow into an internal combustion engine can be regulated to optimize both of these conditions.